use POSIX qw(strftime);

sub uptime {
	local $/ = " ";
	open my $fh, '<', '/proc/uptime'
		or die "Can't open /proc/uptime to read: $!\n";
	return scalar <$fh>;
}

print strftime "Last booted %Y-%m-%d/%H:%M:%S\n", (
	localtime( time() - uptime() )
);